Catalyst solution for electroless deposition of metal on substrate

ABSTRACT

The invention described herein is a catalyst for activating a substrate for the initiation of electroless metal plating and to a process for making the same. The catalyst comprises the product resulting from the admixture of an acid soluble salt of a catalytic metal; the addition product believed to be formed from a solution soluble stannous salt, an acid and urea; and preferably, an extraneous source of halide ions. The catalyst of the invention differs from prior art catalysts in that it has greater stability, does not fume, is lower in cost to make and use and, in the preferred embodiment employing the extraneous source of halide ions, may be operated at lower acidity (high pH) than the prior art catalysts.

[ 1 Apr. 1, 1975 1 CATALYST SOLUTION FOR ELECTROLESS DEPOSITION OF METALON SUBSTRATE [75] Inventors: Michael Gulla, Sherborn; William A.

Conlan, Attleboro, both of Mass.

[73] Assignee: Shipley Company, Inc., Newton,

Mass.

[22] Filed: Nov. 14, 1973 [21] Appl. No.: 415,526

Related U.S. Application Data [63] Continuation-in-part of Ser. Nos.224,742, Feb. 9, 1972, abandoned, and Ser. No. 374,093, June 27,

[52] U.S. Cl 106/1, 117/47 A, 204/30 [51} Int. Cl. C23c 3/00 [58] Fieldof Search 106/1; 117/47 A; 204/30 [56] References Cited UNITED STATESPATENTS 3,627,558 12/1971 Roger et a1. 117/47 R 3,650,913 3/1972DOttavio 117/47 A 3,672,923 6/1972 Zeblisky 106/286 Kuzmik 106/1 Fadgenet al. 106/1 Primary Examiner-Lewis T. Jacobs Attorney, Agent, orFirmDike, Bronstein, Roberts, Cushman & Pfund [57] ABSTRACT Theinvention described herein is a catalyst for activating a substrate forthe initiation of electroless metal plating and to a process for makingthe same. The catalyst comprises the product resulting from theadmixture of an acid soluble salt ofa catalytic metal; the additionproduct believed to be formed from a solution soluble stannous salt, anacid and urea; and preferably, an extraneous source of halide ions, Thecatalyst of the invention differs from prior art catalysts in that ithas greater stability, does not fume, is lower in cost to make and useand, in the preferred embodiment employing the extraneous source ofhalide ions, may be operated at lower acidity (high pH) than the priorart catalysts.

68 Claims, 4 Drawing Figures $n CONTENT (gm) sn+ coNTENT (gm) sum 1 or 2TIME (HRS) FIG.

RATIO UREA: HCI

FIGZ

CATALYST SOLUTION FOR ELECTROLESS DEPOSITION OF METAL ON SUBSTRATECROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of our conending US. patent applications Ser. Nos.224,742 filed on Feb. 9, 1972, now abandoned, and 374,093, filed on June27, 1973.

BACKGROUND OF THE INVENTION 1. Introduction This invention is directedto a formulation for catalyzing a substrate prior to electroless metaldeposition.

2. Description of the Prior Art For electroless plating of substrates,especially for the plating of non-conductive substrates, it has beenknown for some time that chemically plated metal deposits of suitablethickness and adequate bond strength are commercially practical only ifthe substrate surface is properly catalyzed prior to metal deposition.

A common method for catalyzing a substrate prior to plating involvescontact of the substrate with two solutions known in the art as atwo-step catalyst. A process for metallizing utilizing this catalystcomprises contact of a substrate with a first acidic aqueous solution ofa reducing agent such as stannous chloride followed after water rinse bycontact with a second solution of a catalytic metal salt such aspalladium chloride in dilute hydrochloric acid. The adsorbed reducingagent reduces the catalytic metal ions in situ on the substrate surfaceto the catalytic metal thereby providing catalytic sites on the surfacewhich sites are receptive to electroless metal deposition thereon. Thisprocedure is employed successfully in many plating-on-plasticapplications. However, it is subject to various disadvantages includingpoor adhesion between a metallic substrate surface such as copper and asubsequently applied metal deposit. This is especially true where copperis to be deposited over copper such as in the manufacture of printedcircuit boards where copper is deposited over both a plastic substrateand a copper cladding over said plastic substrate. Also, articles in theprocess of being plated using the aforesaid twostep catalyst must bereracked subsequent to catalysis before proceeding to additional stepsin the plating sequence to avoid contamination of the catalyst throughdrag-in from preceding steps and rapid deterioration of the platingbath. Metal plate for decorative purposes obtained using the twostepcatalyst exhibits star dustingi.e., minor imperfections on the surfaceof the metal plate.

An alternative method for catalyzing a substrate prior to electrolessdeposition is also known and is disclosed and claimed in US. Pat. No.3,01 1,920 incorporated herein by reference. In this method, a substrateis contacted with a colloidal catalytic solution formed by the admixturein acid solution of a catalytic metal salt, a stannous salt in molarexcess of the catalytic metal salt and a hydrohalide acid. The catalyticmetal may be selected from the group of silver, gold and the platinumfamily of metals. Palladium is the preferred catalytic metal. The excessstannous salt is responsible for stability of the colloid and preventsit from precipitating out of its suspension. The catalyst operates at apH below about 1 and preferably well below 0. The limitation on the pHis due to the fact that the stannous salt hydrolyzes and precipitates ata pH of about 0.9.

Though this colloidal catalyst has been widely accepted and preferredfor most applications, it is not without some difficulties. One suchdifficulty is the gradual loss of stannous ion in highly acidic solutionby a process believed to involve aerial oxidation with the formation ofstannic ion leading to catalyst instability and subsequent loss. Anothersuch difficulty is the attack of the highly acidic solution of varioussubstrate materials with which the catalyst comes into contact,especially plastic materials including the plastic racks used to carrythe substrate through the plating sequence. Another difficulty is thevolatilization of the hydrohalide acid which is undesirable from ahealth standpoint, corrosion of surroundings, and a quality controlstandpoint. Both of these latter problems would be overcome if thecatalyst formulation could be prepared at a pH higher than the pH of thecatalyst formulations of the prior art.

In US. Pat. No. 3,672,938, there is disclosed a process for catalyzing asubstrate prior to electroless metal deposition with a catalyst alsoformulated by the admixture in acid solution of a catalytic metal salt,a stannous salt in molar excess of the catalytic metal salt and ahydrohalide acid. This catalyst is said to differ from the catalyst ofUS. Pat. No. 3,011,920 in physical form, it being asserted that thecatalyst of said patent is a true solution catalyst rather than acolloidal catalyst as in the aforesaid US. Pat. No. 3,011,920.Regardless of its physical form, it is also highly acidic and suffersthe same disadvantages as the catalyst of said US. Pat. No. 3,011,920.

No attempts are known to have been made in the prior art to prevent theloss of stannous ion by aerial oxidation. Attempts have been made toformulate a low acid, high pH catalyst. Such attempts have beenunsuccessful because the low acid catalyst has been formulated by theexpedient of reducing the hydrohalide acid content. Such a reductionresults in the formation of a precipitate at a pH of about 0.9 for achloride system. This formation of precipitate is believed to be due tohydrolysis of the stannous ions with the formation of insolublehydrolysis products. This results in loss of the catalyst. An example ofthis is shown in the aforesaid US Pat. No. 3,672,938, Example V, wherethere is disclosed a catalyst having a total acid content of onemilliliter of concentrated hydrochloric acid per liter of solution. Thisformulation is of no commercial value as it is of insufficient acidityto solubilize the stannous salt and consequently a stable colloidalcatalyst or stable catalyst in any other form, should it exist, cannotbe prepared.

DEFINITIONS The following definitions are provided to assist in theunderstanding of the ensuing text:

Catalyst formulation is the product resulting from the admixture of anacid soluble salt of a catalytic metal, a stannous salt in molar excesstypically in substantial excess, of the catalytic metal salt, an acid,urea and preferably an extraneous source of halide ions.

Catalyst component refers to any one or more of the salts of thecatalytic metal, stannous salt or acid used in making the catalystformulation.

Addition Product refers to the product that is believed to be formed bythe admixture of the stannous salt, the acid and urea. This is called anaddition product because emperical evidence in connection with theproperties of the catalyst suggests that such an addition product isformed. However, it is possible that only two of the three aforesaidingredients form such an addition product or alternatively, no additionproduct is formed at all, each of the three ingredients existingindependently in solution. Accordingly, as used herein, the termaddition product encompasses the three ingredients used for the purposesset forth herein without limitation as to the manner in which theyinteract, if at all.

Actual halide ion concentration is the concentration of the halide ionsin the catalyst formulation, if any, of the catalyst components used inthe form of a halide. This will be zero if none of the aforesaidcomponents are used in the form of a halide.

Maximum component halide ion concentration is the concentration ofhalide ions that would be in the catalyst formulation if each of thecatalyst components were used in the form of the halide.

Total halide ion. concentration is the required amount of halide ions inthe catalyst formulation in accordance with this invention.

Extraneous halide ions and like terms mean a source of halide ions inaddition to those supplied by the catalyst components. The concentrationof the extraneous halide ions is equal to the difference between thetotal halide ion concentration and the actual halide, ion concentration.

Excess halide ions are halide ions in the catalyst in excess of themaximum component halide ion concentration and the concentration of theexcess halide ions is equal to the difference between the total halideion concentration and the maximum component halide ion concentration.The concentration of the excess halide ions equals the concentration ofthe extraneous halide ions when all of the catalyst components used tomake the catalyst are in the form of the halide.

Precipitation point is the pH at which a precipitate forms in thecatalyst formulation rendering the catalyst unsuitable for use. Thisprecipitate is believed to be hydrolysis products, principally of thestannous salt.

SUMMARY OF THE INVENTION The catalysts described herein are improvementsover catalysts such as those described and claimed in the aforesaid US.Pat. Nos. 3,011,920 and 3,672,938 in that they have greater solutionstability, minimal loss of stannous ion even at low pH, betteradsorption properties, and, if desired, a decreased hydrogen ionconcentration with a correspondingly high pH.

The invention is predicated in part upon the discovery that ureaaddition to the catalyst formulation minimizes stannous ion oxidationloss and consequently, catalyst instability and halide ions play asignificant role in the functioning of the catalyst, the catalyst beingimproved when the concentration of halide ions is increased beyond thatconcentration found in the prior art catalysts by the addition of anextraneous source of halide ions. The improvements resulting from theaddition of urea to the formulation preferably coupled with an excesshalide ion concentration comprise improved stability and adsorptionproperties and solubilization of the stannous salt or retardation of theprecipitation point. Accordingly, catalysts of increased stability andpH can be formulated thereby providing catalyst suitable for use withmaterials readily attacked by strong acids.

A catalyst composition in accordance with this invention comprises theproduct resulting from the admixture of l an acid soluble salt of acatalytic metal, (2)

the addition product formed from a solution soluble stannous salt inmolar excess of the catalytic metal salt,

an, acid urea and preferably (3) an extraneous source of halide ions inan amount sufficient to provide an excess of halide ions in theformulation. The catalyst formulations of this invention have a pH ofless than about 3.5 dependent upon the stannous content as will beexplained in greater detail below.

The product resulting from the admixture of the stan-. nous salt,hydrohalide acid and urea (2 above) as noted above, is believed to bethe addition product which undergoes only minimal dissociation insolution. It appears that as a result of this minimal dissociation, thehydrohalide acid is not available for loss by fuming and the stannousion is unavailable for loss by oxidation. It is an unexpected discoveryof this invention that these components can be used in the form of theaddition product without adversely affecting the propertiesof thecatalyst, even though the product undergoes only minimal dissociation.

In addition to the above, there are unexpected secondary advantages tothe invention. For example, since there is no fuming of the hydrohalideacid, there is essentially no odor associated with the use of thecatalyst. I

cordance with the invention, the results obtainable upon plating-cg,bond strength, take-off, coverage and the like are more reliable andpredictable.

DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 of the drawings is agraphical comparison of stability of a catalyst solution with andwithout the use of the addition product of this invention;

FIG. 2 is a graphical representation of urea content in the formation ofthe addition product as a function of stability;

FIG. 3 graphically represents precipitation point of a series ofcatalysts as a function of pH; and

FIG. 4 graphically represents the precipitation point of a series ofcatalysts as a function of stannous ion concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention set forth hereincomprises a catalyst which includes (1) an acid soluble salt of acatalytic metal, (2) the addition product of a stannous salt solu-. Ible in aqueous solution in molar excess of the catalytic metal, an acidand urea and preferably, (3) an extraneou's source of halide ion in anamount sufficient to provide an excess of halide ions in theformulation.

The catalyst may be formulated substantially with materials and inproportions such as those described and claimed in the aforesaid US.Pat. Nos. 3,011,920

and 3,672,938. The acid soluble salt of the catalytic metal is a salt ofany of those metals known to exhibit catalytic properties in chemicalplating. Such metals include the precious metals, gold and silver andmembers of the platinum family. Palladium is generally found to be themost satisfactory of these catalytic metals for the activation of anon-conducting substrate, particularly a plastic substrate, andtherefore constitutes the preferred embodiment of this invention.Silver, gold and rhodium constitute lesser preferred embodiments of theinvention as some difficulty is encountered in the preparation of thecatalyst due to limited solubility of the silver salts and instabilityof the gold and rhodium salts in solution.

The particular salt of the catalytic metal used is not critical and maycomprise the halides such as those described in the aforesaid U.S. Pat.No. 3,01 1,920 as well as such other salts as the nitrate, sulfate andthe like. Fluoride and iodide salts are lesser preferred. Salts otherthan halides are suitable as halide ions may be introduced into solutionby the extraneous source of halide ions. Preferably, the salt is thehalide having an anion common to that of the other catalyst components.It should be noted that when the halide salt is used, some halide isintroduced into solution, but because of the low concentration of thecatalytic metal salt used, this amount is generally negligible.

The amount of the catalytic metal salt is not critical and is primarilygoverned by cost and functional considerations. Thus, though up to 40 to50 grams per liter or more of the catalytic metal salt is possible, itis desirable to maintain the quantity of the salt as low as possiblefrom a cost consideration without sacrificing the functional propertiesof the catalytic formulation. Typically, the amount of the catalyticmetal salt in the composition does not exceed 8 grams per liter and in amade-up bath, does not exceed 2 grams per liter of solution and morepreferably ranges between about 0.1 and 1 gram per liter of solutionwhen highly concentrated formulations are made, such as formulationscontaining 40 to 50 grams per liter, than the pH of the formulationshould be above 0.5 and the ratio of the stannous ions to the noblemetal ions should be at least 5 to 1.

The particular stannous salt used to formulate the catalyst is likewisenot critical and in addition to a stannous halide, other stannous saltsare suitable such as stannous nitrate and stannous acetate. As with thesalt of the catalytic metal, the stannous halide having an anion commonto that of other catalyst constituents is preferred. When a stannoushalide is used, a source of halide ions is introduced into the catalystformulation though this amount by itself does not provide sufficienthalide ions for purposes of the preferred embodiment of this inventionwhere excess halide ions are used.

The amount of stannous salt used is not critical provided stannous ionsare present in the catalyst formulation in molar excess of the catalyticmetal ions. In this respect, as in the prior art, the molar ratio of thestannous ion to the catalytic metal ion may be as low as 2:1, butpreferably varies between 10:1 and 40:1 and may be as high as 100:1.

The hydrohalide acids, other than hydroiodic acid, are preferred forpurposes of this invention. However, results in terms of stability andcatalytic activity with hydrofluoric acid are marginal. Hydrobromic acidis better and hydrochloric acid provides the best result. Accordingly,the term hydrohalide acid as used herein is intended to mean principallyhydrochloric acid, but also includes hydrohalide acids other thanhydroiodic acid with the realization that these other acids provide onlymarginal results. It should be further realized that the termhydrohalide acid means the presence of hydrogen ions and halide ions insolution though the hydrogen ions may be derived from any other acidthat does not have an anion detrimental to the catalyst formulation.Thus, sulfuric acid, fluoroboric acid and various organic acids such asmaleic acid, as examples, may be used as a source of hydrogen ions withall of the halide ions being supplied by the extraneous source of halideions. Nitric acid should not be used as it forms insoluble additionproducts with urea. Likewise, other acids which form insoluble additionproducts with urea should be avoided.

The amount of acid used may be substantially less than in thecommercially acceptable formulations of the prior art. In the prior art,the concentration of the acid had to be sufficiently high so as toprovide a catalyst having a pH of less than 1 and typically was so highas to provide a catalyst having a pH below 0. Using hydrochloric acid asan example, as much as 12 moles per liter of solution were used. Inaccordance with this invention, though such high concentrations of acidcan be used, the acid concentration can be reduced to a level wherebythe pH of the catalyst is as high as 3.5. Accordingly, for purposes ofthis invention, that amount of acid is used that results in a solutionpH of no greater than 3.5, and in the preferred embodiment of theinvention, the acid is used in an amount sufficient to provide a pHranging between 0.9 and 2.5. It should be noted that though catalystscan be formulated with a pH as high as 3.5, this is principallyaccomplished when the stannous ion concentration is relatively low andthe halide ion concentration is relatively high. Consequently, thestability of catalysts at this high pH is not entirely satisfactory forstorage of catalyst for long periods of time.

The addition product of the stannous salt, acid and urea may be obtainedby mixing the ingredients together when making the catalyst formulationfollowing the procedures of the aforesaid U.S. Pat. No. 3,01 1,920 or anaddition product of the hydrohalide acid and urea may be formed and thenmixed with the stannous salt to form the addition product of the threecomponents. However, if desired, all ingredients may be mixed togetherin a single container also containing the other components of thecatalyst formulation with the addition product believed to be formed insitu. No special reaction conditions such as heating or the like arenecessary.

The addition product is believed to be an adduct of urea which utilizesone molecule of the acid and the stannous compound. Consequently, anexcess of equimolar amounts of urea is preferred relative to the otherconstituents, although less than equimolar amounts also provide somebenefits. The ratio of urea to the hydrohalide acid may vary between1:10 and :1 but preferably varies between 1:1 and 10:1. From thestandpoint of volume only, more urea may be used as the pH of thesolution increases and the volume of acid required threrfore decreases.

Though not wishing to be bound by theory, it is believed that theaddition product used in the formation of the catalyst of this inventionconforms to the structure where X is the halide ion. When an excess ofurea is used, which is preferred for purposes of this invention, theuronium ion will drive the reaction for the formation of the additionproduct to the right, thus preventing dissociation in the catalystsolution. As a result, both the hydrogen halide and the stannous ionsare bound up so that the hydrohalide acid will not fume and the stannousions are prevented from oxidizing to the stannic form.

Decreased oxidation of stannous ion to stannic ion due to the action ofurea as a function of time can be seen by reference to FIG. 1 of thedrawings which is a graphical representation of stannous content as afunction of time for a formulation containing urea (curve A) and onefree of urea (curve B). The formulation of examples l and 2 below wereused to prepare FIG. 1 with air being bubbled through said formulationsin an open beaker to accelerate oxidation. Stannous content wasdetermined periodically. As can be seen from the graph, the oxidation ofstannous ion is substantially retarded by the presence of the urea. Itshould be noted that the curves represented herein are illustrative onlyand only define specifically the systems of examples 1 and 2, otherformulations having different but similar curves. For example, stannousion loss in low acid solution would be reduced even in the absence ofurea.

The concentration of urea relative to the acid concentration is moreimportant for lower pH formulations (below about 0.9 for a chloridesystem) than for higher pH formulations because the tendency of thestannous ion to undergo aerial oxidation is more pronounced in highlyacidic solution. FIG. 2 graphically represents the stannous content of ahighly acidic catalyst (that of example 1) as a function of the ratio ofurea to hydrochloric acid. Measurements were taken after the catalysthad remained standing in an open beaker with air bubbled through for aperiod of forty hours. It can be seen that the greater the ratio of ureato acid, the greater is the concentration of stannous ion left in theformulation.

Though the aforesaid description has referred only to urea, it should beunderstood that halides of urea may also be used though these materialsare less desirable as they are hydroscopic and therefore presentdifficulty in terms of raw materials storage. They are, however,included within the scope of the invention and the term urea as usedherein refers both to urea and its halides.

From the above description, it can be seen that all of the catalystcomponentsi.e., the catalytic metal salt, urea, the stannous salt andthe acid, may or may not be used in the form of their respective halidesthough in a preferred embodiment of the invention, they are all halideshaving a common anion, most preferably chloride. With reference to thedefinitions set forth above, if all catalyst components were in the formof the halide, the resulting halide concentration, referred to as themaximum component halide ion concentration, would not be sufficientlyhigh to obtain the improvements in the stability and adsorptionproperties and the retarded precipitation point. Obviously, if one ormore of the catalyst components were used in a form other than thehalide, then the actual halide ion concentration is still insufficientto obtain the improvements noted above.

In accordance with the preferred embodiments of the invention describedherein, an excess of halide ions is provided in the catalystformulation, above the maximum component halide ion concentration, bythe addi-. tion of an extraneous source of halide ion. The amount of theextraneous halide ions added is equal to at least the difference betweenthe actual halide ion concentration and the required total halide ionconcentration.

In determining the required total halide ion concentration, differentconsiderations apply dependent upon whether the pH of the catalyst isbelow. or above the precipitation point, the pH at which a precipitateforms, which precipitate is believed to be insoluble hydrolysis productsof tin.

With regard first to catalyst formulations having a pH below theprecipitation point in the absence of the ex-: traneous halide ions, thetotal halide ion concentration required is not critical, it beingunderstood that the higher the total halide ion concentration, thegreater will be the stability and adsorption properties of the catalystthough the improvements in these properties are sometimes difficult toascertain, especially with those catalysts having a high hydrogen ionconcentration-e.g., a concentration such that the pH of the catalyst isbelow 0. In general, at a pH below the precipitation point, the totalhalide ion concentration in accor dance with the preferred embodimentdescribed here is at least 0.2 moles in excess of the maximum potentialhalide ion concentration and preferably, at least 0.5 moles in excess.The maximum concentration is not critical and the total halide ionconcentration can be at saturation. Accordingly, halide ionconcentration is at least 0.2 moles in excess of the maximum potentialhalide ion concentration to saturation and preferably is at least 0.5moles in excess to saturation. The concentration of the extraneoussource of halide ions is that amount necessary to increase the actualconcentration of the halide ions to the total concentration of halidethe stannous ions. The relationship between total haI-' ide ionconcentration, pH and stannous ion content is depicted in FIGS. 3 and 4of the drawings for the system palladium chloride (1 gram per literofsolution),

urea (50 grams per liter) stannous chloride, hydrochloric acid andlithium chloride as the source of the extraneous ions. It should beunderstood that other systems are similar to this system though thenumerical limitations defining the curves might differ.

In FIG. 3 of the drawings, there is depicted two families of curves. Thefirst family comprise curves, A, B C.

and D which represent the change in the precipitation point of thecatalyst (pH) as a function of total chloride ion concentration forseveral different stannous .ion

concentrations. The second family of curves, A, B',C and D represent theactual chloride ion concentration derived from the total of the catalystcomponents-the stannous chloride, palladium chloride and hydrochloricacid, but not the lithium chloride. Curves A andA are for a stannous ioncontent of 0.05 moles per liter of solution, B and B for 0.13 moles perliter of solution, C and C for 0.26 moles per liter of solution and Dand D for 0.39 moles per liter of solution. The precipitation point forthis catalyst system in the absence of any extraneous halide ions(lithium chloride) is at a pH of about 0.9. As extraneous chloride ionsare introduced into the system and the total chloride ion concentrationis increased, the precipitation point (pH) is also increased, but not asrapidly for formulations having a low stannous ion concentration (CurveA). Thus, it can be seen that the highest pH (about 3.5) is obtainableonly with the lowest concentration of stannous ion and the highest totalconcentration of chloride ion. As the total chloride ion concentrationdecreases or the stannous ion concentration increases, the highestpossible pH decreases.

The curves of FIG. 3 represent precipitation point. Therefore, the areaabove any given curve represents a stable catalyst while the area belowthe curve represents a catalyst containing a precipitate that is of nocommercial value.

FIG. 3 may be used to determine the amount of ex traneous halide ionrequired for the catalyst formulation. This is determined from theconcentration difference between curves at any given pH and stannous ionconcentration. For example, at a pH of 2 and a stannous ionconcentration of 0.26 moles per liter of solution (Curves C and C), theconcentration difference between curves C and C is about 4.5 so that theconcentration of extraneous chloride ions required to reach theprecipitation point is 4.5 moles per liter of solution. Thus, 4.5 molesof lithium chloride are added to the formulation to provide a totalchloride ion concentration of about 5 moles per liter of solution.However, this chloride ion concentration is only sufficient to reach theprecipitation point of the catalyst and the total chloride ionconcentration should be in excess of this amount to provide a stablecatalyst. In general, for this catalyst system and others within theacope of the invention, the total halide ion concentration should be atleast about 0.2 moles per liter of solution above the halide ionconcentration at the precipitation point of the catalyst and preferablyat least above 0.5 moles per liter of solution above that required atthe precipitation point. The upper limit is not critical and can be thesaturation point of the halide ion in solution. Applying these generalguidelines to the specific formulation depicted in FIG. 3, again makingreference to the example at a pH of 2 and a stannous ion concentrationof 0.26 moles per liter of solution, the total chloride ionconcentration at the precipitation point is 5 moles per liter ofsolution, but to assure the stability, the total chloride ionconcentration should be at least 5.2 moles per liter of solution andpreferably at least 5.5 moles per liter of solution. Accordingly, theconcentration of the extraneous chloride ions-the lithium chloride,added to the formulation should be more than 4.5 moles per liter ofsolution, preferably should be at least 4.7 moles per liter of solutionand more preferably, should be at least 5.0 moles per liter of solution.

With respect to FIG. 3 described above, lithium chloride was selected asthe source of the extraneous chloride ion because of its very highsolubility in solution. Other halide salts are not as soluble. Forexample, when sodium chloride is selected as a source of extraneouschloride ion, the solution becomes saturated when the totalconcentration is about 6.0 moles per liter. This puts a practicallimitation on the maximum pH obtainable as FIG. 3 indicates that whenthe formulation contains 0.39 moles per liter of solution of stannousion, the maximum obtainable pH with 4.5 of total chloride ion is about1.65. When the solution contains only 0.05 moles per liter of solutionof stannous ion, the maximum possible pH is about 2.5 with 4.5 totalmoles of chloride ion.

With regard to the source of the extraneous halide ion, any halide salthaving the requisite solubility properties is suitable provided it doesnot have a cation that would interfere with the functioning of thecatalyst. In this respect, illustrative halide salts that are suitableinclude aluminum chloride, aluminum bromide, magnesium chloride, sodiumchloride, sodium bromide, potassium chloride, potassium bromide, calciumchloride, calcium bromide and the like. Lithium halides are preferredbecause of their solubility and aluminum halides are least preferredbecause such salts tend to interfere with the functioning of thecatalyst.

In FIG. 4 of the drawings, there is graphically presented a family ofcurves showing the precipitation point of the aforesaid palladiumchloride-stannous chlorideurea-hydrochloric acid catalyst system as afunction of the stannous ion concentration at different total halide ionconcentrations. Again, the source of the extraneous halide concentrationnecessary to increase the actual halide ion concentration to the totalhalide ion concentration is lithium chloride. Each curve in the familyof curves is numbered and the numbers proceed from 1 through 8. Eachnumber on the curve is the total halide ion concentration for thatcurve. Each curve represents the precipitation point of the catalystunder consideration and it should be understood that the region to theleft of any given curve represents a useable catalyst and the region tothe right of any given curve represents a catalyst not having a pH inexcess of the precipitation point and one wherein a precipitate hasformed.

From FIG. 4, it can be seen that as the total chloride ion concentrationincreases, as one progresses from Curve No. 1 to Curve No. 8, themaximum possible pH also increases. It can also be seen that theconcentration of the stannous ion becomes more important at the higherpH levels. For example, where the total chloride ion concentration is 8moles per liter of solution, the maximum pH obtainable with 0.4 molesper liter of stannous ion is 2.4 whereas with only 0.5 moles per literof stannous ion, the maximum pH is in excess of 3.5. Since the curves inFIG. 4 represent precipitation point, a slight excess of total chlorideion concentration beyond that represented in the curve is required tomake a catalyst free of precipitate.

It should be noted that at the high pH, the role of the urea is lesscritical than in the highly acidic compositions. Urea provides someimprovement at the higher pH, but the improvement is less dramatic.

Catalysts can be formulated using procedures of the prior art with theextraneous halide ion dissolved in acid solution used to dissolve theother catalyst components, with the addition of urea at any point in theprocess. A preferred method for formulating a catalyst in accordancewith the invention would comprise first preparing a catalyst concentrateusing pre-mixed ureastannous chloride and hydrochloric acid and thendiluting the concentrate when ready for use. In this way, theconcentrate can be made fairly acidic to insure proper dissolution ofthe catalyst components and then the pH can be increased to the extentdesired by dilution. The concentrate would be prepared by firstdissolving the catalytic metal salt in acid solution, then adding thead- 200 ml of each of the above solutions are placed in an open beakerand air is bubbled through each solution at a rate of 10 cubic feet perhour. Periodically, a

small sample of each solution is removed and titrated dition product ofstannous chloride, urea and acid an for tin. The results are graphicallyillustrated in FIG. 1 letting the formulation age. During the ageingprocess, of the drawing which is a plot of stannous content ver-. h lyll rn r m a rk l to gr n to sus time as described above. As can be seenfrom the brown to brown-black coloration evidencing the fordrawing, theformulation of Example 1 set forth herein mation of the colloid.Following ageing, the catalyst lasted for a period in excess of 200hours, at which can, if desired, be diluted with a sodium chloridesolutime, the test was discontinued while the formulation of tionwhereby the pH is raised and the chloride concen- Example 2 of U.S. Pat.No. 3,01 1 ,920 became unstable tration increased. Where a catalysthaving a pH above within about 48 hours when about one-half gram of theprecipitation point is desired, the same procedure stannous ion was leftin solution.

is involved, but as a final step, some of the acid can be As notedabove, the use of excess halide ions permits neutralized with a suitableneutralizing agent, prefera- 15 pH stable catalyst solutions havinglower stannous conbly a weak base such as sodium bicarbonate,centrations than previously possible. The urea addition As alsodisclosed in the above mentioned U.S. Pat. product is also effective instabilizing such solutions, as. No. 3,01 1,920, a stannate such as analkali metal stanshown by the following example: nate may also be addedto the catalyst composition.

The effect ofa stannate salt is to improve the properties EXAMPLE 3 ofthe components thereof and obtain quicker adsorpa. The procedure ofexample 1 is repeated with retion of the catalytic metal on thesubstrate. The manner duction in the amount of stannous chloride to 32grams in which the stannate achieves this result is not fully unperliter of solution (19.2 grams per liter of tin). Upon derstood, but isbelieved to be due to the presence of initial titration, there was foundto be 19.0 grams per. stannic (Sn ions in the formulation. Other sourcesof iter of stannous ion and after 45 OurS of aeration, stannic ions,such as stannic chloride, polystannic acid e e WaS found to be 1 1.3grams per liter of solution. compounds, and the like may be substitutedfor the b. The procedure of example 1 was repeated, but the stannate,with similar results. amount of stannous chloride was reduced to 6%grams The invention will be further exemplified by the folper liter (4.9grams per liter of tin). The catalyst belowing illustrative embodiments.came unstable and a precipitate formed within about ten hours. i EXAMPLEI c. The procedure of example 1 was repeated but the A 1 percent byweight palladium chloride solution is stannous chloride content wasreduced to about 3 prepared by adding one gram palladium chloride tograms perliter (1.8 grams per liter of tin). The catalyst 100milliliters of 0.5N hydrochloric acid. A second sobecame unstable afterabout eight hours. i lution (containing 27.86g of stannous ions) isadded to d. The procedure of example 2 was repeated, but the the first,along with 0.4 g of sodium stannate. To this stannous chloride contentwas reduced to about 15 is added 610 ml of a third solution prepared bymixing grams (9.0 grams per liter tin). The catalyst became 330 ml of12.4N hydrochloric acid with 350 grams of unstable and a precipitateformed in about 6 hours. I urea. The mixture thus contains about 1.4moles of 40 e. The procedure of example 2 was repeated but the urea permole of hydrochloric acid. The mixture is stannous chloride content wasreduced to 6% grams stirred, diluted to 1 liter with water and permittedto per liter (4.9 grams per liter of tin). The catalyst bestand forabout 24 hours. The resultant catalyst formucame unstable within abouttwo hours after make-up. lation is of a dark brown coloration. Nohydrochloric f. The procedure of example 2 was repeated but the acidfumes are detectable. stannous chloride was reduced to 3 grams per liter(1.8

grams per liter of tin). The catalyst became unstable EXAMPLE 2 almostimmediately after make-up. For purposes of comparison, the formulationof Ex- It has been found that it is preferable to use the urea ample 1above is compared with that of Example 2 of in relatively large molarexcess of the hydrohalide acid. U.S. Pat. No. 3,01 1,920 which isreproduced below: The reason for this is believed to be that it preventsdis.- sociation of the addition product. The advantages are illustratedin the following example.

Palladlum chlorlde 1 gram per liter idiochloric acid(12N) EXAMPLE 4sdium stannate 1 V2 grams Six catalyst formulations were preparedaccording to stannous ch1or1de( 1) 37 /2 grams U 335 gram, per mom, theprocedure of example 1, except that the urea content (andcorrespondingly the ratio of urea to hydrochloric acid) was varied so asto show the effect of urea The above ingredients are mixed together inthe upon solution stability. The molar ratio of urea to hyorderindicated and permitted to stand for 24 hours at drochloric acid, andstannous content variation upon about F. exposure to air is set forth inthe following table: 1

Ratio Stannous content (grams/liter) UrcarHCl 0 hours 20 hours 40 hours60 hours hours 011 24.0 12.0 3.5 unstable" unstable 05:1 204 13.5 8.63.2 unstable 1:1 19.6 14.0 11.2 9.4 unstable 2:1 19.9 14.2 14.2 12.3 3.8

To illustrate the relationship between the ratio of urea to hydrohalideacid and stannous content, in the above table, ratio versus stannouscontent at 40 hours is plotted and represented in FIG. 4 as discussedabove. As can be seen from the drawing, the higher the ratio of the ureato the hydrochloric acid, the greater the stannous content is after 40hours of solution aeration.

The above, it can be seen that best results are at the higher ratios ofurea to hydrochloric acid, though as the urea content exceeds 3 molesper mole of hydrochloric acid, little or no improvement is obtained.

Example 5 0.25 grams per liter 3.2 grams per liter 2.5 ml

250 grams per liter 0.5 grams per liter 50 grams per liter to 1 liter ofsolution The above solution had a pH of 1.2. It was stable for in excessof 150 hours with exposure to air as in the manner of example 1.Comparison of this example with example 3, paragraph C, above shows thesubstantially improved results using the higher pH.

A major advantage of a dilute solution such as that of this example 5 iseconomic, especially for plating on plastics where drag-out is aproblem. Also, such solutions can be replenished with fairlyconcentrated solutions without substantial volume growth.

The formulations of this invention find substantially the same use asthe prior art catalytic formulations, such as those disclosed in theaforesaid U.S. Pat. No. 3,011,920. As a specific example of a completeprocessing procedure according to this invention, the following is givenfor a copper-clad plastic laminate substrate provided with through-holesat desired locations:

EXAMPLE 6 l. Precleaning the copper substrate:

a. Clean the substrate by immersion in hot alkaline cleaner, and rinsein clean water.

b. Pickle in an acid bath with an etchant for copper, for example, acupric chloride-hydrochloric acid bath, and rinse.

c. Dip in a 10% volume hydrochloric acid solution to remove residues,and rinse.

'2. Catalysis:

Immerse the clean substrate for 30 seconds or more in the catalystsolution according to example 1 which catalyzes both the copper surfacesand the plastic surherein by reference, for a sufficient time tobuild-up the desired thickness of metallic coating. Rinse thoroughly anddry.

5. Electroplating:

Immerse the coated substrate in a 10% solution of hydrochloric acid toassure a clean copper coating, rinse and electroplate copper over theelectroless coating until a desired thickness is obtained.

With this process, strong uniform coatings of conductive metal areprovided on the substrate on both the plastic surface exposed in thethrough-holes and on the metal surfaces without the necessity ofremoving the metal coating from the cladding prior to electroplating.

EXAMPLE 7 The procedure of example 6 is repeated substituting thecatalytic formulation of example 5 for that of example l with similarresults.

For deposition onto unclad, non-metallic surfaces, the followingprocedure can be employed.

EXAMPLE 8 l. Catalysis:

Immerse the substrate for 30 seconds or longer in the catalyticformulation of example 1 above and rinse.

2. Acceleration:

Immerse the catalyzed substrate in an alkaline accelerator, for example5% sodium carbonate for 1 minute or more, and rinse.

3. Metal Deposition:

Immerse the catalyzed substrate in the desired metal depositionsolution, for example, the formulation of example l of U.S. Pat. No.3,424,597 incorporated herein by reference for a sufficient time tobuild-up the desired thickness of metallic coating. Rinse thoroughly anddry.

EXAMPLES 9-26 Catalyst solutions are made up containing 0.25 g/lpalladium chloride, 10 g/l stannous chloride and 0.5 g/l stannicchloride, and the amounts of the other materials listed below, in enoughwater to make 1 liter. Acrylonitrile-butadiene-styrene plates arescrubbed, rinsed, cleaned with a detergent to remove grease and oil,rinsed, immersed in 10% by volume hydrochloric acid, immersed directlyin the various catalyst compositions for thirty seconds, rinsed,immersed for one minute in a solution of Accelerator 19, available fromShipley Company, rinsed, immersed in an electroless plating bath as inexample 6 and subjected to a final rinse.

The coatings obtained are visually evaluated for completeness, depth,and uniformity of coverage with the results reported below:

Cntinued Each of the above formulations was divided into ten 6 h 4Example Urea Chloride Salt Hcl ggalj portiops (100 ml eac and lithiumchlorlde Number Concentration Concentration Concen. Result e to eac tobrmg the total Concentratlon to a (mole (g (Norm) sired amount. Each ofthe so formed catalyst were then 16 0.1 280 .03 Excell. titrated withsodium bicarbonate to neutralize the acid {g 23 538 g to a point whereturbidity was seen. Thiswas consid- 19 2 4 Exec ered to be theprecipitation point. The chloride introg 18 j E liduced from each of thehydrochloric acid, the stannous 22 8 40 4 g chloride and the lithiumchloride as well as total chlo- 52 0.1 318 KC1 .1 Good l0 ride andprecipitation point are set forth in the follow- 25 8 2 53 ing table.With reference to the table, it should be un- 26 0.1 192 AlCL, ,1 Fairderstood that the chloride concentrations are set forth in moles per 100ml of solution though in FIG. 3 of the drawings, this has been convertedto moles per liter. 15 Moreover, with regard to FIG. 3, the first pointin the EXAMPLES 27 through 30 curve represents a known precipitationpoint for a cata-. These examples illustrate the preparation of thecatalyst having a pH of 0.9 and was derived from formulalyst used forthe derivation of FIGS. 3 and 4 of the tion having a higher initialconcentration of hydrochlodrawings. Four stock solutions were preparedand laric acid.

Solution -l (Cl ((l (Cl" Precipitation ldcntif. 2 Point (pH) 1-1 .100.010 0 .110 1.3 1-2 .100 .010 .090 .200 1.7 1-3 .100 .010 .190 .300 1.9l-4 .100 .0 l 0 .290 .400 2.3 1-5 .100 .010 .390 .500 2.7 1-6 .100 .010.490 .600 3.0 1-7 .100 .010 .590 .700 3.3 l-8 .100 .010 .690 .800 3.52-1 .100 .026 0 .126 I 1.1 1-2 .100 .026 .074 .200 1.4 2-3 .100 .026.174 .200 L4. 2-4 .l0O .020 .274 .400 ll 2-5 .100 .026 .374 .500 2.3 2-6.100 .026 .474 .600 2.5 2-7 .100 .026 .574 .700 2.8 2-8 .100 .026 .674.800 3.1 3-1 .100 .052 0 .152 1.1 3-2 .100 .052 .048 .200 1.3 3-3 .100.052 .148 .300 1.6 3-4 .lO0 .052 .248 .400 L) 3-5 .100 .052 .348 .5002.0 3-6 .100 .052 .448 .600 2.3 I 3-7 .100 .052 .548 .700 2.5 3- 8 .100.052 .648 .800 2.7 4-1 .100 .078 0 .178 1.2 4-2 .100 .078 .022 .200 1.24-3 .100 .078 .122 .300 1.2 4-4 .100 .078 222 .400 1.6 4-5 .100 .078.322 .500. 1.7 4-6 .100 .078 422 .600 1.9 4-7 .100 .078 522 .700 2.0 4-8.100 .078 .622 .800 2.3

belled sequentially 1 to 4. The solutions had composi- The curves ofFIG. 3 are approximations as the pretions as follows: cipitation pointwas observed visually and subject to ex- 5 I f NO 1 2 3 4 perimentalerror. The explanation of the results of this 0 u series of experimentsis set forth above and will not be palladium chloride(gm) 1 1 1 1repeated here. ij ggzg i (gm) %8 g8 Various of .the above formulationswere again pre- Hydrochloric id 37 805 80,6 305 pared though the totalchloride ion concentration was will to 1 liter increased by 0.1 molesper 100 milliliters so that the total chloride ion concentration was inexcess of the The formulations were prepared by dissolving the chlorideion concentration and the precipitation point. palladium chloride in thehydrochloric acid and half Stability of these formulations wasdetermined by purthe water. Stannous chloride was then added very ing aportion of the formulation into a petri dish and slowly with stirringand the resulting solution was perleaving the petri dish exposed to airfor a prolonged pemitted to age until a dark brown coloration was obriodof time. In this way, the catalyst formulation had tained. The remainingwater was then added. The pH of the resulting solution was 0.

a relatively large exposed surface area. The/catalyst was left exposedto air in this manner until such time as a precipitate formed. Theresults obtained are set forth in the following table:

g g gz 5 until a brown coloration was obtained. The solutions were thensplit into three equal 1 liter portions and ad- }1 g ditional sodiumchloride in a given amount was then 5 Yes added to each of the separatesolutions. The catalysts g 58 N0 were then titrated with sodiumbicarbonate to increase 10 the pH and determine the precipitation pointof the cat- 3-1 200 N6 alyst. The following table sets forth solutionidentifigfg cation, chloride content from each of the hydrochloric 4.1200 N acid, stannous chloride and sodium chloride, the total 200 N0chloride content and the precipitation points of the cat- 4-8 200 Noalyst.

Solution (Cl (Cl 1 (CI' (0 Precipitation ldcntif. 2 Point (pH) Thecatalysts having solution identification numbers beginning with l wereless stable than the other catalysts because of the low stannous ionconcentration. Only one of the catalysts exhibited a silver filmcharacteristic of a catalyst left exposed to air for a long period oftime.

To demonstrate the functional properties of the catalyst of theseexamples, the plating sequence of Example 6 above was adopted for theplating of an epoxy copper clad circuit board base material providedwith a random array of through-holes. The catalyst used were thosedescribed in the immediately preceding table. Following the process ofExample 6, each of the tested catalysts formulations provided a stronguniform coating of conductive metal on the plastic surface exposed inthe through-holes and on the backside of the circuit board base materialas well as on the copper clad. There was no necessity for removal of themetal coating over the copper clad material prior to electroplating asthe bond between the copper clad and the electroless copper deposit wasquite strong.

It should be noted that the results obtained here are quite similar tothe results obtained with formulations free of urea as at the relativelyhigh pH used, the function of the urea is of lesser importance.

Examples 31 to 34 The above formulations were prepared by dissolving thepalladium chloride and sodium chloride in one-half of the volume ofwater. The urea was then mixed with stannous chloride and added in aninitial amount such that there was an excess and the balance addedslowly with stirring. The solutions were then permitted to age From theabove, it can be seen that the results obtained are similar to thoseobtained in Examples 1 through 4. Moreover, each of the catalysts setforth in the immediately preceding table were highly effective incatalyzing a substrate in the metallization process described above.

In the aforesaid Examples 31 through 34, the maximum concentration ofextraneous chloride ion is about 4.5 moles per liter of solution becauseof the limited solubility of sodium chloride. Accordingly, using sodiumchloride, the maximum possible pl-l obtainable with 10 grams of stannouschloride per liter of solution is about 2.5.

As with the aforesaid examples, the presence of urea makes a lessdramatic effect on the stability of the formulation because of therelatively high pH employed.

The following are examples of formulations within a substrate followingthe procedure described above.

Example 35 Palladium nitrate (gm) 1 Stannous nitrate (gm) 25 Fluroboricacid (48%-ml) Calcium chloride (gm) Urea (gm) 200 Water to 1 literExample 36 Palladium sulfate (gm) 1 Stannous Sulfate (gm) 25 Sulfuricacid (ml) 20 Calcium bromide (gm) 100 Urea 200 Water to 1 literPalladium chloride (gm) 0.5 Stannous fluroborate( gm) 50 Fluroboric acid(48%-ml) 50 Calcium chloride (gm) 200 -Cont1nued Urea 100 Water to 1liter Example 38 Palladium bromide (gm) 0.50 Stannous bromide (gm) 25Hydrobromic acid (487r-ml) 100 Sodium bromide (gm) 150 Urea 50 Water to1 liter Example 39 Palladium bromide (gm) 0.50 Stannous sulphate (gm) 50Fluroboric acid (487r-ml) 35 Magnesium bromide 250 Urea 250 Water to 1liter Example 40 Gold chloride (gm) 1 Stannous chloride (gm) 25Hydrochloric acid (377z-ml) Sodium chloride (gm) 200 Urea 100 Water to 1liter Example 41 Platinum chloride (gm) l Stannous chloride (gm) 25Hydrochloric acid (377l-ml) 10 Sodium chloride (gm) 200 Urea 100 Waterto 1 liter Example 42 Rhodium sulfate (gm) 1 Stannous sulfate (gm) 25Sulfuric acid (96% ml) 3 Sodium chloride (gm) 200 Urea 100 Water to 1liter Example 43 Palladium chloride (gm) 0.5 Platinum chloride (gm) 0.5Stannous chloride (gm) 25 Hydrochloric acid (37%ml) 25 Sodium chloride(gm) 100 Urea 250 Water to 1 liter EXAMPLES 44 to 46 The followingexamples illustrate a catalyst with a very low stannous ionconcentration:

All of the above were made according to the process of Example 37. Theformulation of Example 44 was stable in a petri dish exposed to air fora period of 105 hours, the formulations of Example 45 was stable forperiod of 83 hours and that of Example 46 for a period of 72 hours.

While the particular embodiments of the present invention have beenshown and described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects. Therefore, it is intended that thespecification be interpreted as illustrative only, and not in anylimiting sense.

We claim:

1. A catalyst composition for catalyzing a substrate prior toelectroless metal deposition thereon, said catalyst compositioncomprising the product resulting from the admixture of an acid solublesalt of a catalytic metal selected from the group consisting of silver,gold and the platinum family metals, a solution soluble stannous salt inmolar excess of the catalytic metal salt, a hydrohalide acid sufficientto provide a pH less than 1 and urea in an amount such that the molarratio of the ure to the hydrohalide acid exceeds 1 to 10.

2. The composition of claim 1 where the catalytic metal salt is a memberof the platinum family of metals.

3. The composition of claim 2 where the catalytic metal salt does notexceed 8 grams per liter of solution.

4. The composition of claim 1 where the catalytic metal salt variesbetween 0.1 and 5 grams per liter of solution.

5. The composition of claim 4 where the acid is selected from the groupconsisting of hydrochloric acid and hydrobromic acid.

6. The composition of claim 4 where the acid is hydrochloric acid.

7. The composition of claim 6 where the catalytic metal salt is apalladium salt.

8. The composition of claim 6 where the catalytic metal salt ispalladium chloride. 7

9. The composition of claim 8 also containing an alkali stannate salt.

10. The composition of claim 1 where the molar ratio of the stannoussalt to the catalytic metal salt varies between 2:1 and :1. l

11. The composition of claim 10 where the ratio va ries between 10:1 and40:1.

12. The composition of claim 1 where the molar ratio of urea tohydrohalide acid varies between 1:10 and 13. The composition of claim 12where the ratio varies between 1:1 and 10:1.

14. A catalyst composition for catalyzing a substrate prior toelectroless metal deposition thereon, said catalyst comprising theproduct of admixture of palladium chloride, stannous chloride in molarexcess of the palladium chloride, hydrochloric acid sufficient toprovide a pH less than 1 and urea in an amount such that the molar ratioof urea to hydrochloric acid exceeds 1 to l0.

15. The composition of claim 14 where the palladium chloride does notexceed 8 grams per liter of solution.

16. The composition of claim 14 where the palladium chloride variesbetween 0.1 and 5 grams per liter of solution.

17. The composition of claim 14 also containing an alkali stannate salt.

18. The composition of claim 14 where the molar ratio of the stannouschloride to palladium chloride varies between 211 and 100:1.

19. The composition of claim 18 where the ratio va-.

ries between 10:1 and 40:1.

20. The composition of claim 14 where the molar ratio of urea tohydrochloric acid varies between 1:10

and 100:1.

21. The composition of claim 20 where the molar ratio varies between 1:1and 10:1.

22. A catalyst composition for catalyzing a substrate prior toelectroless metal deposition thereon, said composition comprising theproduct resulting from the admixture of (1) a salt of a catalytic metalselected from the group of gold, silver and the platinum family metalsalts, (2) the addition product formed from a stannous salt in an amountsuch that the stannous ion concentration is in molar excess of thecatalytic metal ion concentration, an acid in an amount sufficient toprovide a pH less than about 3.5 and urea in an amount such that themolar ratio of urea to the acid exceeds 1 to 10, and (3) a halide saltin an amount such that the' total halide ion concentration at a pH belowthe precipitation point of the catalyst is at least 0.2 moles per literin excess of the concentration of halide ions provided by all othercomponents and at a pH at or above the precipitation point is at leastsufficient to prevent the formation of a precipitate.

23. The composition of claim 22 where the pH is below the precipitationpoint and the total halide ion concentration is from 0.2 moles in excessof the concentration of halide ions provided by all other catalystcomponents to saturation.

24. The composition of claim 23 where the total halide ion concentrationis from 0.5 moles in excess of the concentration of halide ions from allother catalyst components to saturation.

25. The formulation of claim 22 where the pH is at or above theprecipitation point and the total halide ion concentration varies fromat least 0.2 moles in excess of that required to prevent formation of aprecipitate to saturation.

26. The composition of claim 25 where the total halide ion concentrationvaries from at least 0.5 moles in excess of that required to preventformation of a precipitate to saturation.

27. The composition of claim 22 where all halide ions are chloride ions.

28. The composition of claim 27 where the pH varies between about 0.9and 3.5.

29. The composition of claim 27 where the pH varies between about 0.9and 2.5.

30. The composition of claim 22 where the molar ratio of the stannousion from the stannous salt to the catalytic metal ion from the salt ofthe catalytic metal varies between 2:] and 100:1.

31. The composition of claim 30 where the ratio varies between about :1and 40:1.

32. The formulation of claim 22 where the catalytic metal salt ispalladium chloride.

33. The composition of claim 22 where the molar ratio of urea to acidvaries between 1:10 and 100:1.

34. The composition of claim 33 where the ratio varies between 1:1 and10:1.

35. A catalyst composition for catalyzing a substrate prior toelectroless metal deposition thereon, said composition comprising theproduct of admixture of l) a catalytic metal halide salt selected fromthe group of a gold halide, a silver halide and a platinum family metalhalide, the concentration of said catalytic metal halide not exceeding50 grams per liter of solution (2) the addition product formed from astannous halide in an amount such that the stannous ion concentration isin molar excess of the catalytic metal ion concentration, the molarratio of said stannous ion to said catalytic metal ion varying between2:1 and 100:1, a hydrohalide acid in an amount sufficient to provide aformulation having pH less than about 3.5 and urea in an amount suchthat the molar ratio of urea to acid exceeds 1:10 and (3) a halide saltin an amount such that the total halide ion concentration at a pH belowthe precipitation point of the catalyst is at least 0.2 moles per literin excess of the concentration of halide ions provided by all othercatalyst components and at a pH at or above the precipitation point ofthe catalyst, is at least sufficient to prevent formation of aprecipitate.

36. The composition of claim 35 where all of the halide ions arechloride ions.

37. The composition of claim 36 where the pH is below the precipitationpoint and the total chloride ion concentration is from 0.2 moles inexcess of the concentration of chloride ions provided by all othercatalyst components to saturation.

38. The composition of claim 37 where the total chloride ionconcentration is from 0.5 moles in excess of the concentration ofchloride ions provided from all other catalyst components to saturation.

39. The composition of claim 36 where the pH is at or above theprecipitation point of the catalyst and the total chloride ionconcentration varies from at least 0.2 moles in excess of that requiredto prevent formation of a precipitate to saturation.

40. The composition of claim 39 where the total chloride ionconcentration varies from at least 0.5 moles in excess of that requiredto prevent formation of a precipitate to saturation.

41. The composition of claim 36 where the pH varies between about 0.9and 3.5.

42. The composition of claim 36 where the pH varies between about 0.9and 2.5.

43. The composition of claim 36 where the molar ratio of the stannousion to catalytic metal ions varies between about 10:1 and 40:1.

44. The composition of claim 43 where the catalytic metal salt ispalladium chloride.

45. The composition of claim 36 where the molar ratio of urea tohydrochloric acid varies between 1:10 and :1.

46. The composition of claim 45 where the ratio varies between 1:1 and10:1.

47. A catalyst composition for catalyzing a substrate prior toelectroless metal deposition thereon, said composition comprising theproduct of admixture of (l) palladium chloride in an amount notexceeding 50 grams per liter of solution, (2) the addition productformed from stannous chloride in an amount such that the stannous ion isin molar excess of the palladium ion concentration, the molar ratio ofsaid stannous ion to said palladium ion varying between 2:1 and 100:1,hydrochloric acid in an amount sufficient to provide a compositionhaving a pH less than about 3.5 and urea in an amount such that theratio of urea to acid exceeds 1:10 and (3) a chloride salt in an amountsuch that the total chloride ion concentration at a pH below theprecipitation point of the catalyst is at least 0.2 moles per liter inexcess of the concentration of the balance of the chloride ions providedby all other catalyst components and at a pH at or above theprecipitation point of the catalyst, is at least sufficient to preventthe formation of a precipitate.

48. The composition of claim 47 where the pH is below the precipitationpoint and the total chloride ion concentration is from 0.2 moles inexcess of the concentration of chloride ions provided by all othercatalyst components to saturation.

49. The composition of claim 48 where the total chloride ionconcentration is from 0.5 moles in excess of the concentration ofchloride ions from all other catalyst components to saturation.

S0. The composition of claim 47 where the pH is at or above theprecipitation point and the total chloride ion concentration varies fromat least 0.2 moles in excess of that required to prevent formation of aprecipitate to saturation.

51. The composition of claim 50 where the total chloride ionconcentration varies from at least 0.5 moles in excess of that requiredto prevent formation of a precipitate to saturation.

52. The composition of claim 47 where the pH varies between about 0.9and 3.5.

53. The composition of claim 47 where the pH varies between about 0.9and 2.5.

54. The composition of claim 47 where the molar ratio of the stannousions to the palladium ions varies between about :1 and 40:1.

55. The composition of claim 47 where the chloride salt is selected fromthe group consisting of aluminum chloride, magnesium chloride, sodiumchloride, potassium chloride, calcium chloride and lithium chloride.

56. The composition of claim 55 where the chloride salt is sodiumchloride.

57. The process for stabilizing a catalyst for catalyzing a substrateprior to electroless metal deposition, said catalyst comprising theproduct of (l) catalytic metal ions, (2) stannous ions in an amount inmolar excess of said catalytic metal ions, (3) halide ions and (4)hydrogen ions in an amount sufficient to provide a formulation having apH less than about 3.5, said process comprising adding urea to saidcatalyst composition, the concentration of urea being such that themolar ratio of the urea to the hydrogen ions is at least 1 to 10.

58. The process of claim 57 where the catalytic metal ions are palladiumions in a concentration not exceeding 8 grams per liter.

59. The process of claim 58 where the stannous ions are derived fromstannous chloride and the molar ratio 63. The process of claim 61 wherethe pH varies between about 0.9 and 2.5.

64. The process of claim 61 where the pH is below the precipitationpoint of the catalyst and the total chloride ion concentration is from0.2 moles in excess of the concentration of chloride ions provided byall other catalyst components to saturation.

65. The process of claim 64 where the total chloride ion concentrationis from 0.5 moles in excess of the concentration of chloride ionsprovided by all other catalyst components to saturation.

66. The process of claim 63 where the total chloride ion concentrationis at least 0.2 moles in excess of that required to prevent theformation of a precipitate to saturation.

67. The composition of claim 63 where the total chloride ionconcentration is at least 0.5 moles inexcess of that required to preventformation of a precipitate to saturation.

68. The process of claim 57 where the concentration of urea is such thatthe molar ratio of urea to acid varies

1. A CATALYST COMPOSITION FOR CATALYZING A SUBSTRATE PRIOR TOELECTROLESS METAL DEPOSITION THEREON, SAID CATALYST COMPOSITIONCOMPRISING THE PRODUCT RESULTING FROM THE ADMIXTURE OF AN ACID SOLUBLESALT OF A CATALYTIC METAL SELECTED FROM THE GROUP CONSISTING OF SILVER,GOLD AND THE PLATINUM FAMILY METALS, A SOLUTION SOLUBLE STANNOUS SALT INMOLAR EXCESS OF THE CATALYTIC METAL SALT, A HYDROHALIDE ACID SUFFICIENTTO PROVIDE A PH LESS THAN 1 AND UREA IN AN AMOUNT SUCH THAT THE MOLARRATIO OF THE UREA TO THE HYDROHALIDE ACID EXCEEDS 1 TO
 10. 2. Thecomposition of claim 1 where the catalytic metal salt is a member of theplatinum family of metals.
 3. The composition of claim 2 where thecatalytic metal salt does not exceed 8 grams per liter of solution. 4.The composition of claim 1 where the catalytic metal salt varies between0.1 and 5 grams per liter of solution.
 5. The composition of claim 4where the acid is selected from the group consisting of hydrochloricacid and hydrobromic acid.
 6. The composition of claim 4 where the acidis hydrochloric acid.
 7. The composition of claim 6 where the catalyticmetal salt is a palladium salt.
 8. The composition of claim 6 where thecatalytic metal salt is palladium chloride.
 9. The composition of claim8 also containing an alkali stannate salt.
 10. The composition of claim1 where the molar ratio of the stannous salt to the catalytic metal saltvaries between 2:1 and 100:1.
 11. The composition of claim 10 where theratio varies between 10:1 and 40:1.
 12. The composition of claim 1 wherethe molar ratio of urea to hydrohalide acid varies between 1:10 and100:1.
 13. The composition of claim 12 where the ratio varies between1:1 and 10:1.
 14. A catalyst composition for catalyzing a substrateprior to electroless metal deposition thereon, said catalyst comprisingthe product of admixture of palladium chloride, stannous chloride inmoLar excess of the palladium chloride, hydrochloric acid sufficient toprovide a pH less than 1 and urea in an amount such that the molar ratioof urea to hydrochloric acid exceeds 1 to
 10. 15. The composition ofclaim 14 where the palladium chloride does not exceed 8 grams per literof solution.
 16. The composition of claim 14 where the palladiumchloride varies between 0.1 and 5 grams per liter of solution.
 17. Thecomposition of claim 14 also containing an alkali stannate salt.
 18. Thecomposition of claim 14 where the molar ratio of the stannous chlorideto palladium chloride varies between 2:1 and 100:1.
 19. The compositionof claim 18 where the ratio varies between 10:1 and 40:1.
 20. Thecomposition of claim 14 where the molar ratio of urea to hydrochloricacid varies between 1:10 and 100:1.
 21. The composition of claim 20where the molar ratio varies between 1:1 and 10:1.
 22. A catalystcomposition for catalyzing a substrate prior to electroless metaldeposition thereon, said composition comprising the product resultingfrom the admixture of (1) a salt of a catalytic metal selected from thegroup of gold, silver and the platinum family metal salts, (2) theaddition product formed from a stannous salt in an amount such that thestannous ion concentration is in molar excess of the catalytic metal ionconcentration, an acid in an amount sufficient to provide a pH less thanabout 3.5 and urea in an amount such that the molar ratio of urea to theacid exceeds 1 to 10, and (3) a halide salt in an amount such that thetotal halide ion concentration at a pH below the precipitation point ofthe catalyst is at least 0.2 moles per liter in excess of theconcentration of halide ions provided by all other components and at apH at or above the precipitation point is at least sufficient to preventthe formation of a precipitate.
 23. The composition of claim 22 wherethe pH is below the precipitation point and the total halide ionconcentration is from 0.2 moles in excess of the concentration of halideions provided by all other catalyst components to saturation.
 24. Thecomposition of claim 23 where the total halide ion concentration is from0.5 moles in excess of the concentration of halide ions from all othercatalyst components to saturation.
 25. The formulation of claim 22 wherethe pH is at or above the precipitation point and the total halide ionconcentration varies from at least 0.2 moles in excess of that requiredto prevent formation of a precipitate to saturation.
 26. The compositionof claim 25 where the total halide ion concentration varies from atleast 0.5 moles in excess of that required to prevent formation of aprecipitate to saturation.
 27. The composition of claim 22 where allhalide ions are chloride ions.
 28. The composition of claim 27 where thepH varies between about 0.9 and 3.5.
 29. The composition of claim 27where the pH varies between about 0.9 and 2.5.
 30. The composition ofclaim 22 where the molar ratio of the stannous ion from the stannoussalt to the catalytic metal ion from the salt of the catalytic metalvaries between 2:1 and 100:
 31. The composition of claim 30 where theratio varies between about 10:1 and 40:1.
 32. The formulation of claim22 where the catalytic metal salt is palladium chloride.
 33. Thecomposition of claim 22 where the molar ratio of urea to acid variesbetween 1:10 and 100:1.
 34. The composition of claim 33 where the ratiovaries between 1:1 and 10:1.
 35. A catalyst composition for catalyzing asubstrate prior to electroless metal deposition thereon, saidcomposition comprising the product of admixture of (1) a catalytic metalhalide salt selected from the group of a gold halide, a silver halideand a platinum family metal halide, the concentration of saiD catalyticmetal halide not exceeding 50 grams per liter of solution (2) theaddition product formed from a stannous halide in an amount such thatthe stannous ion concentration is in molar excess of the catalytic metalion concentration, the molar ratio of said stannous ion to saidcatalytic metal ion varying between 2:1 and 100:1, a hydrohalide acid inan amount sufficient to provide a formulation having pH less than about3.5 and urea in an amount such that the molar ratio of urea to acidexceeds 1:10 and (3) a halide salt in an amount such that the totalhalide ion concentration at a pH below the precipitation point of thecatalyst is at least 0.2 moles per liter in excess of the concentrationof halide ions provided by all other catalyst components and at a pH ator above the precipitation point of the catalyst, is at least sufficientto prevent formation of a precipitate.
 36. The composition of claim 35where all of the halide ions are chloride ions.
 37. The composition ofclaim 36 where the pH is below the precipitation point and the totalchloride ion concentration is from 0.2 moles in excess of theconcentration of chloride ions provided by all other catalyst componentsto saturation.
 38. The composition of claim 37 where the total chlorideion concentration is from 0.5 moles in excess of the concentration ofchloride ions provided from all other catalyst components to saturation.39. The composition of claim 36 where the pH is at or above theprecipitation point of the catalyst and the total chloride ionconcentration varies from at least 0.2 moles in excess of that requiredto prevent formation of a precipitate to saturation.
 40. The compositionof claim 39 where the total chloride ion concentration varies from atleast 0.5 moles in excess of that required to prevent formation of aprecipitate to saturation.
 41. The composition of claim 36 where the pHvaries between about 0.9 and 3.5.
 42. The composition of claim 36 wherethe pH varies between about 0.9 and 2.5.
 43. The composition of claim 36where the molar ratio of the stannous ion to catalytic metal ions variesbetween about 10:1 and 40:1.
 44. The composition of claim 43 where thecatalytic metal salt is palladium chloride.
 45. The composition of claim36 where the molar ratio of urea to hydrochloric acid varies between1:10 and 100:1.
 46. The composition of claim 45 where the ratio variesbetween 1:1 and 10:1.
 47. A catalyst composition for catalyzing asubstrate prior to electroless metal deposition thereon, saidcomposition comprising the product of admixture of (1) palladiumchloride in an amount not exceeding 50 grams per liter of solution, (2)the addition product formed from stannous chloride in an amount suchthat the stannous ion is in molar excess of the palladium ionconcentration, the molar ratio of said stannous ion to said palladiumion varying between 2:1 and 100:1, hydrochloric acid in an amountsufficient to provide a composition having a pH less than about 3.5 andurea in an amount such that the ratio of urea to acid exceeds 1:10 and(3) a chloride salt in an amount such that the total chloride ionconcentration at a pH below the precipitation point of the catalyst isat least 0.2 moles per liter in excess of the concentration of thebalance of the chloride ions provided by all other catalyst componentsand at a pH at or above the precipitation point of the catalyst, is atleast sufficient to prevent the formation of a precipitate.
 48. Thecomposition of claim 47 where the pH is below the precipitation pointand the total chloride ion concentration is from 0.2 moles in excess ofthe concentration of chloride ions provided by all other catalystcomponents to saturation.
 49. The composition of claim 48 where thetotal chloride ion concentration is from 0.5 Moles in excess of theconcentration of chloride ions from all other catalyst components tosaturation.
 50. The composition of claim 47 where the pH is at or abovethe precipitation point and the total chloride ion concentration variesfrom at least 0.2 moles in excess of that required to prevent formationof a precipitate to saturation.
 51. The composition of claim 50 wherethe total chloride ion concentration varies from at least 0.5 moles inexcess of that required to prevent formation of a precipitate tosaturation.
 52. The composition of claim 47 where the pH varies betweenabout 0.9 and 3.5.
 53. The composition of claim 47 where the pH variesbetween about 0.9 and 2.5.
 54. The composition of claim 47 where themolar ratio of the stannous ions to the palladium ions varies betweenabout 10:1 and 40:1.
 55. The composition of claim 47 where the chloridesalt is selected from the group consisting of aluminum chloride,magnesium chloride, sodium chloride, potassium chloride, calciumchloride and lithium chloride.
 56. The composition of claim 55 where thechloride salt is sodium chloride.
 57. The process for stabilizing acatalyst for catalyzing a substrate prior to electroless metaldeposition, said catalyst comprising the product of (1) catalytic metalions, (2) stannous ions in an amount in molar excess of said catalyticmetal ions, (3) halide ions and (4) hydrogen ions in an amountsufficient to provide a formulation having a pH less than about 3.5,said process comprising adding urea to said catalyst composition, theconcentration of urea being such that the molar ratio of the urea to thehydrogen ions is at least 1 to
 10. 58. The process of claim 57 where thecatalytic metal ions are palladium ions in a concentration not exceeding8 grams per liter.
 59. The process of claim 58 where the stannous ionsare derived from stannous chloride and the molar ratio of stannous ionsto palladium ions varies between 2:1 and 100:1.
 60. The process of claim59 where the ratio varies between 10:1 and 40:1.
 61. The process ofclaim 57 where the hydrogen ions are derived from hydrochloric acid. 62.The process of claim 61 where the pH varies between about 0.9 and 3.5.63. The process of claim 61 where the pH varies between about 0.9 and2.5.
 64. The process of claim 61 where the pH is below the precipitationpoint of the catalyst and the total chloride ion concentration is from0.2 moles in excess of the concentration of chloride ions provided byall other catalyst components to saturation.
 65. The process of claim 64where the total chloride ion concentration is from 0.5 moles in excessof the concentration of chloride ions provided by all other catalystcomponents to saturation.
 66. The process of claim 63 where the totalchloride ion concentration is at least 0.2 moles in excess of thatrequired to prevent the formation of a precipitate to saturation. 67.The composition of claim 63 where the total chloride ion concentrationis at least 0.5 moles in excess of that required to prevent formation ofa precipitate to saturation.
 68. The process of claim 57 where theconcentration of urea is such that the molar ratio of urea to acidvaries between 1:1 and 10:1.